Generation of photofluorescent materials by short wavelength ultraviolet irradiation of non-fluorescent bis-diarylchloromethyl-1,3,4-oxadiazoles

ABSTRACT

A system for the transcription of expressions comprising a member incorporating a non-luminescent material transformable to a photoluminescent material by transcriptive light-activation of short-wavelength which resultant fluorescent transcription is made discoverable by light-activation of longer wavelength.

United States Patent 1' n 3,869,363 Singh' Mar. 4, 1975 GENERATION OF PHOTOFLUORESCENT v MATERIALS BY SHORT WAVELENGTH ULTRAVIOLET IRRADIATION OF NON-FLUORESCENT BIS-DIARYLCHLOROMETHYL-1,3,4- OXADIAZOLES Balwant Singh, Stamford, Conn.

American Cyanamid Company, Stamford, Conn.

Filed: Dec. 13,1973 Appl. 'No.: 424,268

Inventor:

Assignee:

References illed UNITED STATES PATENTS Dorion 250/271 Primary Examiner-Howard S. Williams Attorney, Agent, or Firm-Charles J. Fickey [57] ABSTRACT which resultantfluorescent transcription is made discoverable' by light-activation of longer wavelength.

10 Claims, N0 Drawings solve a problem may be limited by its method of synthesis. The synthesis of fluorescent compounds from a non-luminous precursor compound by wet, methods placed limitations upon the practical commercial use of fluorescence in transcription of expressions for communicative purposes and information retrieval. Much of the resurgence of interest in luminescence inthe past few years has been concerned with the development of systems for storage and retrieval of information for communicative purposes. Prior to the instant invention transcription of expressions by wetless methods was hindered by the very methods of synthesis of fluorescent compounds. With the instant invention nonluminous precursor compounds are transformed to fluorescent compounds by the application of shortwavelength light which transformed compounds will fluoresce upon light-activation of longer wavelength;

2 acters, code markings such as dots or lines, or pictorial representations.

In the present invention, storage of information is rapid, accurate and wetless, no fixing being required. Retrieval is rapid, exceptionally sensitive and accurate and is not accompanied by degradation. The inventive technique combines photochemical transcription of ex- This wetless synthesis of fluorescent compounds has now made the use of fluorescence more practicable for transcription of expressions for communicative purposes.

Information storage and recovery systems are of rapidly increasing importance in the present-day economy in view of the exponential rise in thenumber and complexity of the data which must be 'recordedand be retrievable to handle the increasing everyday business load,-and to assist in scientific developments. Many optical systems, including those based on silver halide emulsions and the like, have contributed significantly to this development, largely because of the high packing density with good retrievable resolution inherent in such systems. Systems based on magnetic means, e.g., the well-known magnetic tape and magnetic ink checkprinting systems, have likewise found great utility, largely because of the relatively simple equipment in volved, combined with, particularly in the case'of the tapes, high reproduciblefidelity. However, the optical systems are not as versatile as desired in that only a single image is normally recorded at any one bit, e.g., the developed Ag image. The same is true of the magnetic tape images where normally only the magnetic image is obtained at any one bit. This image can be made visual by a separate step, e.g., by dusting with iron powder. The magnetic ink images have the advantage of being both visually and magnetically sensible; however, these images suffer from a relatively low packing density.

It will be understood that transcription of expressions may be of any desired type, that is, alphanumeric char- Non-Fluorescent I pressions, allowing fine resolution, with detection by fluorescence (more sensitive than absorption). As mentioned, no fixing is required where the fluorescer precursor is only sensitive to light of wavelength of 2,537 A. or less. v

A system for storing and retrieving information is disclosed in copending, commonly assigned application,

Ser. No. 848,578, filed Aug. 8, 1969, now abandoned, which is a continuation-in-part of application Ser. No. 764,312, filed Oct. 1, 1968, now abandoned, which comprises the following: a non-fluorescent material X, capable of photoconversion to a fluorescent material Y, wherein Y has an absorption band of wavelength longer than the longest wavelength band of X, is irradiated with an informationcontaining beam of light of such a wavelength to convert the image portion-of ma terial X to the fluorescent material Y. A longer wavelength stimulating light radiation is then applied to cause compound Y to fluoresce and thus display the image which can be detected visually or by suitable instrument. Thus material X may be considered as a fluorescer precursor.

For this purpose suitable compounds disclosed in the copending application, among others, are 2-(2-furyl or thienyl)-3-acylchromones of the formula;

.where R is phenyl, lower alkylphenyl, lower alkoxyphemethyl-2-thienyl-3-anisoylchromone are included since f w o e their photolysis mechanism, upon exposure to ultraviolet light is substantially the same as that of the 2-(2-furyl)-3-acylchromones.

The preparation of these chrornones is described in greater detailin copending, commonly assigned'application Ser. No. 859,607, filed Aug. 8, 1969 which is a continuation-in-part of application Ser. No. 764,294,

filed Oct. 1, 1968. v

I have now found a new group of compounds which undergo phototransformation to a form in which they are florescent. These compounds are cyclic azo compounds with sublating substituents which undergo a photochemical sublation in accordance with the following equation:

Fluorescent l N==N where S, and S represent the sublating substituents, chlorine, bromine or Co Bu, R 'and R represent the remnants, diarylmethyl or fluorence Radical, and V represents an oxygen, sulfur or N-Z where-N represublation, double bonds are formed at each nucleic carbon of the heterodiazole flve membered ring providing new fluorescent cyclic azo compounds by wetless synthesis.

The same reaction takes place when such compounds are compounds are raised to their melting point, since they decompose at that point.

Cyclic azo compounds which are within the scope of the invention may be represented-by the formula:

i "i 5 Md 3, i l l, N N (A) B a where V represents an oxygen, sulfur or N-Z'where N represents nitrogen and Z represents a lower alkyl, alkaryl or aryl radical, and S and S represent the sublating substituents, chlorine, bromine or -Co Bu. Ultraviolet irradiation with shortwavelength 2,537 A. light of compounds A and B respectively produces the highly colored and highly fluorescent bisdiarylmethylene-Z, 5-dihydro-l, 3, 4-oxadiazole and fluoryloxadiazol.

As previously indicated the same reaction occurs under heat, such as infrared radiation or direct contact heat, for example. The radiant source may be of various types providing ultra-violet or infra-radiation including lamps, electric arcs, or ultra-violet and infrared lasers. The image can be formed in any well known manner as by focusing a radiant beam, projecting a beam through a stencil, by use of'moving mirror systerns with lasers and the like. Detectable fluorescence is obtained by exposure for less than a second, and even as lowas nanoseconds to milliseconds.

The inventive method may be used to replace any process that employs change of optical density to change an electrical signal. This may include electronic storage and replay'of sound and pictures, numerical data collection and retrieval, and the like; and to produce and validate cards, stamps, passes, mail and the like documents. The fluorescer precursor X may be a colorless material, as may also the converted .material Y. In this instance, the storage and retrieval may be unknown to all persons except those intended to have knowledge of the information storage. This could be used for placing information on passes or documents to be retained by one person and checked or authenticated by another such as in the case of a gate pass. An advantage of the present system is that any portion or entire cards or documents can be treated with fluorescer precursor material X, even over other information or images, after which particular information may be put on the treated part by light projection, infrared radiation, or hot die stamping. It will be apparent therefore, that many cards may be produced, with individual information placed thereon at a later time, by conversion of the desired image portion to a fluorescent compound Y. Since the compounds are colorless in either state, space is saved in that the later information is printed over the original visible information. Detection is preferably, as

rial; This stimulating radiation is of such a wavelength thatit does not convert any of the remaining material X to material Y. Although this is the preferable'mode of operation in order to prevent conversion of the background to the same state as the image by the detecting radiation, where the detection is relatively of short duration, this could be done by the same wavelength radiation as used to form the image.

The present material has a further characteristic that the amount of detectable fluorescence is proportional to the amount of latent fluorescer which has been converted to the fluorescent state. The amount converted on any radiated area depends on theduration of time of exposureto the irradiating energy. The longer the time period is, the more latent fluorescer there will be converted per unit of exposed area and thus the more intense the fluorescence upon subsequent radiation and detection. This characteristic makes it possible to produce detectable variable tone fluorescent radiation over a given area. This is much like the tone variation in a photographic negative or a magnetic sound tape. Thus the present invention could be used to prepare a sound tape by audio modulationof the radiant source. The sound is detectable by conventional fluorescent detection means coupled to audio output means by a suitable transducer. A sound track could be put on a movie film in the same manner, either beside the pic- 1 ture, or printed directly on the film. A phonograph disc a fluorescent bar," and creating another word ornumber adjacent thereto in fluorescer precursor material X. This, of course, is limited to the area of the object which has been treated with fluorescer precursor material X.

The fluorescer precursor material X may be coated on any desired substrate such as paper, glass, wood, plastic, cloth, leather, and the like, or it maybe incorporated in transparent or opaque plastic films. The substrate may be of any configuration, i.e.,.sheets, belts, discs, drums, three dimensional objects, such as bottles, boxes, and the like. Techniques for this will be readily apparent to persons skilled in the art. It will be obvious intended use.

5 The fluorescer p resursor material X may be any cyclic azo compound as described above which has the desired properties, that is it has a' non-fluorescent form which absorbs light, or heat, to be converted to a form in which it fluoresces under. light of a longer wavelength than that used for conversion to the fluorescent form.

The invention will be further described and illustrated by the following specific examples which are representative of the wide variety of photosensitive chromones provided thereby.

EXAMPLE 1 v in this Example, a solution of his 5% diphenylchloromethyl-1,3,4-oxadiazol in a copolymer was coated as a thin film of 0.3 mil thickness on white paper stock. The copolymer was a Geon 222 (Goodrich Rubber Co; a copolymer of polyvinyl chloride and polyvinylidene chloride; The film shows no color or fluorescence. When the substrate was irradiated with a short wavelength ultraviolet mercury light (H- 1 O mercury light, 2537), the film was converted to the compound bis-diphenylmentylene-2,5-dihydro-1,3,4- oxadiazole, which was a bright pink color under ordinary light, and exhibited a red fluorescence under longer wavelength ultraviolet radiation.

EXAMPLE 2 A polyvinyl chloride solution having 5% bisdiphenylchloromethyl-l,3,4-oxadiazole was used to treat a paper substrate. The substrate was irradiated with a short wavelength ultraviolet light of 2,537 A. as in Example l, with the same results.

I claim:

1. A method for the transcription of expressions'to a member incorporating a cyclic azo compound of the formula:

l (non-luminescent) 2 I by directed photochemical short-wavelength light generation of a fluorescent cyclic azo compound, in situ', of the formula:

( luminescent) which fluorescent transcription is made discoverable by longer wavelength radiation; wherein R, and R represent a symmetrical bis aromatic methyl or polycyclic aromatic radical remnant and S and S respectively represent sublating substituents chlorine, bromine or -CO BU and V represents oxygen, sulfur or N-Z where N represents nitrogen and Z represents lower alkyl, alkaryl or aryl.

2. The non-luminescent compound of claim 1 7 wherein said compound is symmetrical bis-diary]- substrate.

9. The method of claim l wherein more than one non-luminescent in said member.

l0.- The method of claim 1 wherein said nonprecursor compound is incorporated luminescent compound is incorporated in a liquid vehi- 

1. A METHOD FOR THE TANSCRIPTION OF EXPRESSIONS TO A MEMBER INCORPORATING A CYCLIC AZO COMPOUND OF THE FORMULA:
 2. The non-luminescent compound of claim 1 wherein said compound is symmetrical bis-diarylhalomethyl-1,3,4-oxadiazole.
 3. The non-luminescent compound of claim 1 wherein said compound is symmetrical bis fluorenylhalo-1,3,4-oxadiazole.
 4. The method of claim 1 wherein said light of shortwavelength is ultraviolet light of about 2,537 A. or less.
 5. The method of claim 1 wherein said long-wavelength radiation has a wavelength greater than about 2,537 A.
 6. The method of claim 1 wherein said member is a substrate.
 7. The method of claim 1 wherein said member is a film.
 8. The method of claim 1 wherein said member is a light-transmittant plastic.
 9. The method of claim 1 wherein more than one non-luminescent precursor compound is incorporated in said member.
 10. The method of claim 1 wherein said non-luminescent compound is incorporated in a liquid vehicle. 